Crossword Genius

Drink quite a lot, initially drunk (7)

Ross

I believe the answer is:

tequila

'drink' is the definition.
(tequila is a kind of drink)

'quite a lot initially drunk' is the wordplay.
'initially' indicates taking the first letters.
'drunk' is an anagram indicator.
The initial letter of 'lot' is 'l'.
'quite'+'a'+'l'='quiteal'
'quiteal' anagrammed gives 'TEQUILA'.

(Other definitions for tequila that I've seen before include "Cocktail -- 1988 American crime film -- equaliser units (anag)" , "Mexican liquor made from agave" , "Is there another drink to equal it?" , "Mexican tipple" , "Mexican alcoholic drink" .)

I've seen this clue in The Telegraph.
Want a hint initially instead of a full solution? Install my app